Method and means for preventing amplifiers from oscillating



R. A. HEISING.

METHOD AND MEANS FOR PREVENTINGYAMPLIFIERS FROM OSCILLATING. APPLICATJION FILED FEB. I4. I918.

l ,42 6 ,73 3, Patented Aug. 22, 1922.

" a citizen of the United States,

UNITED STATES PATENT OFFICE.

RAYMOND" A.'HEIsING, 0E EAST ORANGE, NEW JERsEx AssrGNoR TO WESTERN ELEcT Io' COMPANY, INCORPORATED,

OF NEW YORK. 1

OF NEW YORK, N. Y., A CORPORATION METHOD AND MEANS FOR PREVENTING; AMPLIFIERS FROM IOSCILLATING.

T all whom it may concern: I

Be it known that I, RAYMOND" A. I-IEISING,

residin at East Orange, in the county of Essex,

Means for Preventing Amplifiers from Oscillating,of "which the following-is a full clear, concise, and-exact description.

This invention relates to thermionic'am plifiers or repeaters, and the object of the invention is to provide simple methods and .means whereby a thermionic tube or audion "used to amplifyalternating current, and

particularly high frequency alternating current, can be kept fromoscillating-with period or periods of its own, owing to the" [capacity coupling between the grid and the "plate or' other elements 'ofthe tube. In case" a tube so tends to oscillate and its ratio of amplificationis sufficiently high,"its own oscillations may be magnified to such a high degree asto interfer'ewith the amplifying action of the tube or'produce undesired frequencies in the output. In general, then, the 1object0'f the inv'e'ntion'is to so proportion the parts of an inherently coupled amplifier circuit as to preventit from oscillating.

When an amplifier tends to set up oscil lations due to its inherent coupling, it has been found that this action can ordinarily be prevented-by properly proportioning the parts'of the circuit. In the case of a tube may be determinedeither expernnentally or If the coilresis tances are negligibleythe eiiective output inductance-- having an inductive input circuit and an output circuit, oscillations due to grid-plate coupling can be prevented by making the output circuit inductance of sufficiently large value. The'value necessary will in general depend upon certain constants of the circuit,

for instance, the internal impedance, the capacity between grid and plate, the input and output coil resistances and the effectlve inductance of the input circuit. The proper.

value of inductance in the output circuit necessary to accomplish the object stated,

by calculation.

' must bear the same or a greater ratio to the effective input inductance as the ratio of Specification of'Lette'rs Patent. P t t g. 2 1922. Application filed February 14,,"1913; Serial No. 217,139.

.ties, may also tend to cause oscillations which maybe prevented, as, for example, in the "manner hereinafter set forth. tate :of New Jersey, have invented certain new and useful Improvements in Methods and plate coupling; Fig. 2 illustrates diagrammatically the essentials of the circuit of Fig.1 1 when it tends to'actas an oscillator due to such coupling; Fig. 3 is a corresponding diagramof a vacuum tube circuit in which the grid-filament and plate-filament capacitlesare illustrated.

In'Fig. 1, a source of alternating current 1-1s connected to an amplifying tube A of the audion type. The source 1 may be any suitable means, as, for example, an oscillation generator of the audion type. An inductance L in circuit with source '1 is coupled to an inductance L in the input circuit 2 of tube A, which will have an amplified current variation in its output circuit 3 in which is located coil L coupled to coil L, located in an antenna 4 for impressing oscillations upon the antenna to cause the electromagnetic waves to be radiated. In

case greater power is desired, one or more additional tubes A, as shown in dotted lines, may be placed in parallel with tube A,

that is, with the grids, filaments and plates respectively, of-the tubesjconnected. The usual heating battery 5 and output battery '6- are provided. Battery 6 may be placed in series with choke coil 7 and be shunted about condenser 8, through which high frequency current will pass.

An inductance of proper magnitude placed in the output circuit 3 will preventiree oscillations of the tube circuit due -to gr1d-plate coupling. Inductance L should ordinarily not be larger than is necessary to accomplish the desired result. It is unnecessary that the inductance be a separate coil L as the same result may obviously be obtained if the self-inductance of coil L is sufiiciently large.

Fig. 2 represents the circuit of Fig. l in a simplified term, and shows a tube A with input inductance L output inductance L the grid-plate'capacity being diagrammatically shown by a connecting capacity 0 The frequency of oscillations set up will depend upon capacity G and inductances L and L If L ismade sufiiciently large,

55? freexoscillations.

no oscillations resultas the energy to the' input will tatement 3 enough amplification of any'e'xisting oscillations to cause them to continue. a 5 In Eig B the capacity g represents the uted capacity of inductance L Thus two tuned circuits X aiidY are formed tvhich,

ft tuned to :the same i or approximately ;the

i: Afto act asa;generator. Inorderl to prea vent such generation, thevcircuits' and Y 5, sihfouldgbe: @tuned to; different frequencies, in mhic case oscillations Willnot lie-generated. f This" can be readiiy accomplished by adding a a small capacity C in;,par-allel= with the ljfcapacity c or-as shown in parallel with The desired result will be obtained in gieither. case. Itishou-ld be understood that; the; arrangements of Figs; 2 and 3' are not i alternative or mutually"exclusive ibut are;

directedvlito counteracting difierent but an{ 25,1alogous causes of,- oscillationsyand both may bevf applied-toa singlejsystem if both thosewastes-- ins e si s p i y r a ii nductance to prevent oscillations, the resist-V I anoe ofithe circuit mayibei-ncreasedasshown 3Q in HeisingPate'nt 1,199,180ydated Septem v, V th re whic om ri e u r yin th -p ulse sto .be repeated tothe control electrode of said device andfthereby establishin variations in, potential across. said catho e. and

anode leading off the; established variations. exclusively to the outgoing circuitcexcept {fort such variations as are supplied to} the a .-vent .free v-oscillations such as are due to ing "v- -ternal capacity coupling of .thetubeor other .itendency ;of -,the circuit to oscillate. J hat is claimed is y I 40 1 The-method of; }repeating and amplifyi ding substantially vvithout distortion" with a ,thermionic. device comprising. a vacuum tube having; cathode, anode and control electrodes therein which -comprises supplying the im; pulses toi-bej repeated -.to thecontrol electrode of said device aiid ;;thereby establishing vari- :rthrough the coupling, between the electrodes ;:.'internal;-of :said tube, and in: compensating- 1 tfori said: icoupling and thereby preventing;

2. A transmission,systemtadapted to am plifyi'iv BQVfiSilIP substantiallythe same ,form as .ximy are areceived' 'comprising means-for pre- -.lventin"gi :free oscillations in at vacuum tube soli'amplifieriihaving negligible external input? i Jandi'out ut resistance; which means consists iibctive' inductance in the output cir-g (fof an e cuitaa liavingsa ratio @130; the efiective induc r tance ofirtliesinputzcircuit not less'than'sthe amplifying ratio of the tube.

fed back to cause H I am"ieque y,1;wi111tend to cause Ltheltube, y n I transmit high frcquency, carrier Waves in ,4 'l hedi vent onis not limited in its applie 1 cationic radio systems i butmay be generally applied, wherethermionicaudiondevices are gi aused as amplifiers and. itiisdesired to pre- A transmission system adapted to amance, said means consisting of inductance inthe output circuit sufiicientIY I Ig I plilfy waves in"substantiall rthezsame form as they are Jre'ceiv'edw'ic'omprisingfmeansj for pretivelyi to the efi'ective inductance of the in- 'putcirciiit "toaccjomplish the said preventing. ,i

.4. A transmission; systernf. adapted to ceived comprising: a. three element vacuum tube amplifier having aniou tput circuit, said" tube also having an linducti've :input circilit and aninternal capacitycoupling and said output circuit, including an inductance: ap-

proximatelyiequ-al to the effective inductance.

of said input circuitmultiplied by the amplificationratio of said tube, to prevent said tube acting :a's z'an" independent generator of oscillations, While permitting the transmission thronghj said inductance" of said high frequency waves. Q

5. The method of repeati g} and amplifylingl substantially without 4 distortion with a thermionic device comprising 1 a vacuum tube having; cathode,ianode andcontrolelectrodes control electrode circuit; "of said] device preventingffree:oscillations. p

6. A transmission system comprising-1 an incoming line-aadapted tossupply high frequenfcv weak impulses f'to. be.;.amplified,l I an wutgoing line adapted to transmit said im" 5 .ations' in potential, across said cathode and l anode, leading off the-established variations 'exc'lusively-t o;thev outgoing circuit except j;

pulses; substantiallywithoutjgi distortion and saidglinessaidamplifier comprising an electron discharge device having Icathode,'= any fla a V. i- 'with said grid and-cathode; said devicehav- ;ing 3 an 'input' and an I output'circuit coupled substantially wholly through -thecapacityof said electrodes, and an inductancevin said' a source of potential-in circuit output circuit and cooperating with} said capacity ,toprfevent said amplifier from-gen eratingi free oscillations, while permitting saijd high frequency impulses to flow throng said indu an e, I it i I Invwitnessi mhe O- i h re ii o :my nameathi's;Ethiday of=February AAED, v 1918. i v

antenna-131m. 

